The present invention generally relates to overflow preventing valve apparatuses, and more particularly to an overflow preventing valve apparatus provided at a final end of a fluid supplying system in a fluid supplying apparatus constructed to release the locking operation with respect to a pilot valve which is in an open state for controlling open and closed states of a main valve to close the pilot valve, in a case where the main valve closes in response to the closing of a stop valve within a fluid supplying system passage, for example, in addition to a case where a dangerous fluid level indicating possible occurrence of overflow is detected.
Generally, a fluid supplying apparatus for supplying fluid to a tank rulley and the like from a storage tank, is provided with a flowmeter for measuring a predetermined flow quantity of fluid disposed within a fluid supplying system passage, a stop valve, and an overflow preventing valve having a drop pipe, provided at a final end of the fluid supplying system passage. When fluid of predetermined quantity is supplied into a tank of the tank rulley, the stop valve is automatically closed due to a signal supplied from the flowmeter for measuring a predetermined flow quantity of fluid, to stop the fluid supplying operation. Furthermore, in a case where the fluid supplying apparatus becomes inoperative and the fluid is excessively supplied into the tank to possibly introduce an overflow state, the overflow preventing valve detects the abnormal fluid level and closes, to stop the fluid supplying operation.
The conventional overflow preventing valve is constructed to drive and close the main valve provided at the inner part of the fluid supplying apparatus by use of a driving source such as hydraulic and pneumatic sources, when the overflow preventing valve detects the abnormal fluid level within the tank. Accordingly, a driving source is required exclusively for driving to open and close the main valve. Therefore, the construction of the apparatus became complex, and there was a disadvantage in that the operational cost became high.
Hence, in order to eliminate the above described disadvantages, the present applicant has previously proposed an overflow preventing valve provided with a pilot valve, in which the pilot valve is opened and closed to open and close the main valve. According to the above overflow preventing valve, the locking operation with respect to the pilot valve in the open state can be positively released to close the pilot valve and then close the main valve, even in a case where a pressure signal obtained as a result of detecting the abnormal fluid level is of a very small pressure value. Thus, the main valve can be closed without requiring a special driving source.
However, in the above proposed overflow preventing valve, the main valve closes automatically when the fluid supplying operation is stopped due to the closing of a stop valve provided within the fluid supplying system passage, but the pilot valve remains locked in the open state. Accordingly, the fluid within a chamber provided with the pilot valve leaks to the side of a drop pipe, and excessive fluid is supplied into the tank. Hence, there was a problem in that degradation is introduced in the accuracy of the operation to supply fluid of predetermined quantity. Moreover, the fluid leaks outside the tank from the drop pipe when the drop pipe is transferred to another tank, and was especially dangerous when the fluid is gasoline and the like.
Accordingly, a method can be considered in which a special manipulation lever is provided at an outer part of the overflow preventing valve, and the manipulating lever is manipulated when the stop valve closes to release the locking operation with respect to the pilot valve and close the pilot valve. However, this method is troublesome in that the manipulation lever must be manipulated every time the fluid supplying operation is completed with respect to each tank, and the operation efficiency accordingly becomes low. In addition, there is a possibility for the operator to forget to manipulate the above manipulation lever, and should this situation occur, the same problems introduced in the above case are then introduced.